c++ - 错误的错误代码

Question

我正在使用 portaudio 来播放声音。我希望能够通过 UI 选择输出。我是这样管理的:

PaError err = Pa_Initialize();
if( err != paNoError )
    return false;

qDebug() <<"Port audio succeed initialization !";

int numDevices;

numDevices = Pa_GetDeviceCount();
if( numDevices <= 0 )
{
    qDebug() << "ERROR: Pa_CountDevices returned " << numDevices;
    return false;
}

const PaDeviceInfo *deviceInfo;
bool isThereOutput = false;
int i = 0;
while(i < numDevices and !isThereOutput)
{
    deviceInfo = Pa_GetDeviceInfo( i );
    isThereOutput = (deviceInfo->maxOutputChannels > 0);
    i++;
}
if(!isThereOutput)
{
    qDebug() << "No output device";
    return false;
}

PaError errorOpening;

if(outputDevice != "")
{
    PaStreamParameters outputDeviceInfo;
    int numDevices = Pa_GetDeviceCount();

    const   PaDeviceInfo *deviceInfo;
    for(int i = 0; i<numDevices; i++ )
    {
        deviceInfo = Pa_GetDeviceInfo( i );
        if(deviceInfo->maxOutputChannels > 0 && deviceInfo->name == outputDevice)
        {
            outputDeviceInfo.device = i;
            outputDeviceInfo.channelCount = 1;
            outputDeviceInfo.sampleFormat = paInt8;
            outputDeviceInfo.suggestedLatency = deviceInfo->defaultLowOutputLatency;
        }
    }

    if(outputDeviceInfo.channelCount > 1)
    {
        errorOpening = Pa_OpenStream(&stream, NULL, &outputDeviceInfo, SAMPLE_RATE, FRAME_PER_BUFFER, paNoFlag, audioCallback, this);
    }

}

if(outputDevice == "" or errorOpening != paNoError)
{
    if(errorOpening != paNoError)
        qDebug() << "Can't open selected device ("<< outputDevice <<"), switching to the default one. Error : " << Pa_GetErrorText(errorOpening);
    errorOpening = Pa_OpenDefaultStream( &stream,
                      0,            /* no input channels */
                      1,            /* mono output */
                      paInt8,       /* 8 bits output */
                      SAMPLE_RATE,
                      FRAME_PER_BUFFER, /* frames per buffer, i.e. the number
                                              of sample frames that PortAudio will
                                              request from the callback. Many apps
                                              may want to use
                                              paFramesPerBufferUnspecified, which
                                              tells PortAudio to pick the best,
                                              possibly changing, buffer size.*/
                      audioCallback, /* this is your callback function */
                      this ); /*This is a pointer that will be passed to
                                                       your callback*/
}

if(errorOpening != paNoError)
    return false;

if(Pa_StartStream( stream ) != paNoError)
    return false;

它失败了:

Can't open selected device ( "Sortie intégr" ), switching to the default one. Error : Invalid error code (value greater than zero)

但我不明白为什么 OpenStream 会失败并显示一个奇怪的错误代码，而 Pa_OpenDefaultStream 却能正常工作。

所以:

• 为什么会失败？
• 为什么会抛出错误的错误代码？

Answer 1

我假设您使用 C++(尽管您的代码中有几个奇怪的 and 和 or。)

如果您的 for 循环没有找到任何满足 eviceInfo->maxOutputChannels > 0 && deviceInfo->name == outputDevice 的 PaDeviceInfo ，那么您的 outputDeviceInfo 将被未初始化。这意味着它的 channelConnect 可以有任何值，包括大的负值。然后 Pa_OpenStream 不会被调用，您的 errorOpening 也会被未初始化。我敢打赌，当您将其输入 Pa_GetErrorText() 时，这就是 Invalid error code (value greater than zero) 的原因。